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Ghosh O.,Seth Anandram Jaipuria College | Ghosh T.,Maharaja Manindra Chandra College | Chatterjee T.N.,Dinabandhu Andrews College
Solar Physics | Year: 2014

We studied the predictability of the 10.7 cm solar radio flux by using stationary and non-stationary time-series analysis techniques of fractal theory to find the correlation exponent, the spectral exponent, the Hurst exponent, and the fluctuation exponent of the time series. The Hurst exponent was determined, from which the fractal dimension and consequently the predictability was evaluated. The results suggest that stationary methods of analysis yield inconsistent result, that is, amongst the four techniques used, the values of the exponents show great disparity. While two of the techniques, namely the auto-correlation function analysis and the spectral analysis, indicate long-term positive correlation, the other two methods, specifically the Hurst rescaled range-analysis and the fluctuation analysis, clearly exhibit the anti-correlated nature of the time series. The two non-stationary methods, that is, the discrete wavelet transform and the centered moving-average analysis, yielded values of the Hurst exponent that are indicative of positive correlation, of persistent behavior, and also showed that the time series is predictable to a certain extent. © 2013 Springer Science+Business Media Dordrecht. Source

Sasmal S.,University of Calcutta | Hazra S.,University of Calcutta | Kundu P.,Maharaja Manindra Chandra College | Dutta S.,Indian Association for The Cultivation of Science | And 3 more authors.
Inorganic Chemistry | Year: 2011

This investigation presents the syntheses, crystal structures, magnetic properties, and density functional theoretical modeling of magnetic behavior of two heterobridged μ-phenoxo-μ 1,1-azido dinickel(II) compounds [Ni II 2(L 1) 2(μ 1,1- N 3)(N 3)(H 2O)]•CH 3CH 2OH (1) and [Ni II 2(L 2) 2(μ 1,1-N 3)(CH 3CN)(H 2O)](ClO 4)•H 2O•CH 3CN (2), where HL 1 and HL 2 are the [1 + 1] condensation products of 3-methoxysalicylaldehyde and 1-(2-aminoethyl)-piperidine (for HL 1)/4-(2-aminoethyl)-morpholine (for HL 2), along with density functional theoretical magneto-structural correlations of μ-phenoxo-μ 1,1-azido dinickel(II) systems. Compounds 1 and 2 crystallize in orthorhombic (space group Pbca) and monoclinic (space group P2 1/c) systems, respectively. The coordination environments of both metal centers are distorted octahedral. The variable-temperature (2-300 K) magnetic susceptibilities at 0.7 T of both compounds have been measured. The interaction between the metal centers is moderately ferromagnetic; J = 16.6 cm -1, g = 2.2, and D = -7.3 cm -1 for 1 and J = 16.92 cm -1, g = 2.2, and D(Ni1) = D(Ni2) = -6.41 cm -1 for 2. Broken symmetry density functional calculations of exchange interaction have been performed on complexes 1 and 2 and provide a good numerical estimate of J values (15.8 cm -1 for 1 and 15.35 cm -1 for 2) compared to experiments. The role of Ni-N bond length asymmetry on the magnetic coupling has been noted by comparing the structures and J values of complexes 1 and 2 together with previously published dimers 3 (Eur. J. Inorg. Chem. 2009, 4982), 4 (Inorg. Chem. 2004, 43, 2427), and 5 (Dalton Trans. 2008, 6539). Our extensive DFT calculations reveal an important clue to the mechanism of coupling where the orientation of the magnetic orbitals seems to differ with asymmetry in the Ni-N bond lengths. This difference in orientation leads to a large change in the overlap integral between the magnetic orbitals and thus the magnetic coupling. DFT calculations have also been extended to develop several magneto-structural correlations in this type of complexes and the correlation aim to focus on the asymmetry of the Ni-N bond lengths reveal that the asymmetry plays a proactive role in governing the magnitude of the coupling. From a completely symmetric Ni-N bond length, two behaviors have been noted: with a decrease in bond length there is an increase in the ferromagnetic coupling, while an increase in the bond lengths leads to a decrease in ferromagnetic interaction. The later correlation is supported by experiments. The magnetic properties of 1, 2, and three previously reported related compounds have been discussed in light of the structural parameters and also in light of the theoretical correlations determined here. © 2011 American Chemical Society. Source

Guha A.,University of Calcutta | Banu K.S.,University of Calcutta | Banerjee A.,University of Calcutta | Ghosh T.,University of Calcutta | And 3 more authors.
Journal of Molecular Catalysis A: Chemical | Year: 2011

Three new mono-manganese(II) complexes of a compartmental ligand, namely [Mn(HL)(H2O)3](NO3)2·H 2O (1), [Mn(HL)(SCN)2(H2O)]·H 2O (2), and [Mn(HL){N(CN)2}(H2O) 2](NO3)·H2O (3), where L = 2,6-bis{2-(N-ethyl)pyridineiminomethyl}-4-methylphenolato, have been synthesized and characterised by routine physicochemical techniques and complexes 1, 2 also by X-ray single crystal structure analysis. All the mono nuclear complexes contain MnII high spin species at octahedral core as evidenced by magnetic moment (measured at 300 K) and EPR study at 77 K. As revealed by crystal structure analyses, the protonation of one imine nitrogen atom of the potential dinucleating ligand L hampers to form the expected dinuclear Mn II complex. However, complexes 1-3 show excellent catecholase-like activity with both 3,5-di-tert-butylcatechol and tetrachlorocatechol as substrates. In addition complexes 1 and 2 also exhibit phosphatase activity, while 3 forms an adduct with p-nitrophenyl phosphate as substrate. To the best of our knowledge this is the first report of MnII complexes being able to catalyze the oxidation of TCC to TCQ. Catecholase and phosphatase activities have been monitored by UV-vis spectrophotometer and Michaelis-Menten equation has been applied to rationalize all the kinetic parameters where complex 1 shows maximum kcat value followed by 2 and 3 (where for phosphatase activity 3 only forms an adduct). © 2011 Elsevier B.V. All rights reserved. Source

Majumdar L.,Indian Center for Space Physics | Das A.,Indian Center for Space Physics | Chakrabarti S.K.,Indian Center for Space Physics | Chakrabarti S.K.,se National Center For Basic Science | And 2 more authors.
Research in Astronomy and Astrophysics | Year: 2012

One of the stumbling blocks for studying the evolution of interstellar molecules is the lack of adequate knowledge about the rate coefficients of various reactions which take place in the interstellar medium and molecular clouds. Some theoretical models of rate coefficients do exist in the literature for computing abundances of complex pre-biotic molecules. So far these have been used to study the abundances of these molecules in space. However, in order to obtain more accurate final compositions in these media, we have calculated the rate coefficients for the formation of some of the most important interstellar pre-biotic molecules by using quantum chemical theory. We use these rates inside our hydro-chemical model to examine the chemical evolution and final abundances of pre-biotic species during the collapsing phase of a proto-star. We find that a significant amount of various pre-biotic molecules could be produced during the collapse phase of a proto-star. We thoroughly study the formation of these molecules via successive neutral-neutral and radical-radical/radical-molecular reactions. We present the time evolution of the chemical species with an emphasis on how the production of these molecules varies with the depth of a cloud. We compare the formation of adenine in interstellar space using our rate-coefficients and using those obtained from existing theoretical models. Formation routes of the pre-biotic molecules are found to be highly dependent on the abundances of the reactive species and the rate coefficients involved in the reactions. The presence of grains strongly affects the abundances of the gas phase species. We also carry out a comparative study between different pathways available for the synthesis of adenine, alanine, glycine and other molecules considered in our network. Despite the huge abundances of the neutral reactive species, production of adenine is found to be strongly dominated by the radical-radical/radical-molecular reaction pathways. If all the reactions considered here contribute to the production of alanine and glycine, then neutral-neutral and radical-radical/radical-molecular pathways are both found to have a significant part in the production of alanine. Moreover, radical-radical/radical-molecular pathways also play a major role in the production of glycine. © 2012 National Astronomical Observatories of Chinese Academy of Sciences and IOP Publishing Ltd.. Source

Gupta M.D.,Maharaja Manindra Chandra College
Transportation Research Part D: Transport and Environment | Year: 2014

Carbon footprint is intricately related with the consumption and lifestyle pattern of individuals. The transport sector is one of the major sectors that effects lifestyle in a significant way and is the major contributor towards the city emissions. This paper attempts to estimate the carbon footprint arising from household's use of road transport in the city of Kolkata across various income categories. The objective is to see how the footprint changes across income categories and also what factors drive changes in the footprint values across the defined income categories. The study has been based on primary surveys done across the city of Kolkata by choosing about 500 households across various income classes defined. Estimation of carbon footprint shows a clear picture of the relation between people's affluence and the average per capita footprint. It clearly shows that per capita footprint from transport use increases with income. Further results show that income, vehicle ownership and per capita transport expenditure has significant and positive impact on per capita footprint of households from road transport use. © 2014 Elsevier Ltd. Source

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